1. Field of the Invention
The present invention relates to a method of cutting a workpiece such as a semiconductor wafer using a cutting apparatus having two cutting blades equipped therewith.
2. Related Arts
Referring to FIG. 5, a semiconductor wafer W has a plurality of cross streets S to define a lattice pattern thereon, each square area having a circuit pattern formed thereon. The semiconductor wafer W can be diced into a plurality of square chips C.
Referring to FIG. 6, such a semiconductor wafer W is attached to a holder frame F by using a piece of adhesive sheet T, and the wafer-and-frame combination is fixedly supported by a chuck table 11. Then, a cutting means 20 is lowered in the Z-axial direction until its cutting blade 24 has reached the surface of the semiconductor wafer W, and the chuck table 11 is moved in the X-axial direction while the cutting blade 24 is rotated at an increased speed. Every time the cutting in the X-axial direction has been finished, the cutting means 20 is moved the street-to-street distance in the Y-axial direction for indexing, and then, the cutting in the X-axial direction is repeated.
Referring to FIGS. 7 and 8, the cutting means 20 comprises a housing 22, a rotary shaft 23 rotatably supported by the housing 22, the rotary shaft 23 having a blade mount 23a integrally connected to its end, a fastening nut 27 to be mated with the male threads 23b formed on the blade mount 23a, and a cutting blade 24 to be fixed to the mount 23a by fastening with the nut 27. The cutting blade 24 comprises an annular hub 24a and a cutting edge 24b integrally connected to the annular hub 24a. As seen from FIG. 6, the cutting bade 24 is covered by a blade casing 26, and a pair of coolant supply nozzles 25 are so positioned that cooling water may flush to the place at which the cutting is being effected.
Some cutting apparatuses, as for instance, disclosed in Japanese Patent 11-26402(A) use two cutting means such as shown in FIGS. 6, 7 and 8. Referring to FIG. 9, the first cutting blade 24 is fixed to the end of the first rotary axis 26 whereas the second cutting blade 61 is fixed to the end of the second rotary axis 60. These rotary axes 26 and 60 are aligned in line so that the first and second cutting blades 24 and 61 confront each other. With this arrangement the two cutting blades 24 and 61 can be used simultaneously in cutting the semiconductor wafer W. The efficiency with which the workpiece can be cut is increased substantially thanks to simultaneous use of two cutting blades, permitting two streets to be cut simultaneously.
According to the cutting method disclosed in Japanese Patent 11-26402(A), at the outset the cutting edge 24b of the first cutting blade 24 is aligned with one of the outermost opposite streets of a circular workpiece whereas the cutting edge 61b of the second cutting blade 61 is aligned with the other outermost street, as shown in FIG. 10. These cutting blades 24 and 61 are moved stepwise toward each other by the street-to-street distance L2 every time two streets have been cut.
The first and second cutting means 20 and 21 are constructed as shown in FIGS. 6, 7 and 8. Therefore, these cutting means cannot be put close to each other, leaving a minimum distance L1 (equal to the total thickness of their hub projections 24a and 61a), which is larger than the street-to-street distance L2 in the intermediate zone D of the workpiece W. As a matter of fact, the minimum edge-to-edge distance L1 is 5 times as large as the street-to-street distance L2, thus preventing the simultaneous cutting of two streets in the intermediate zone D. Therefore, one of the first and second cutting blades 24 and 61 is used in the intermediate zone, and accordingly, the cutting efficiency is lowered.
Referring to FIG. 11, the first cutting edge 24b is aligned with the outermost street of the side zone E of the workpiece W whereas the second cutting edge 61b is aligned with the center street of the intermediate zone D of the workpiece W. The cutting of two lines or streets S is repeated every time these cutting edges 24b and 61b have been moved the street-to-street distance in the xe2x88x92Y-axial direction for indexing. The workpiece such as a semiconductor wafer is a circle, and therefore, the X-axial stroke of the first cutting edge 61b in the intermediate zone D is much longer than that of the second cutting edge 24b. The X-axial stroke of the second cutting edge 24b must be extended beyond the circle to be equal to the longer stroke of the first cutting edge 61b. This will cause the second cutting edge 24b to run a significant length of useless stroke, and accordingly the cutting efficiency will be lowered.
One object of the present invention is to provide a method of cutting a workpiece at an increased efficiency or a dual-cutting method devoid of useless strokes of cutting blades across a workpiece.
To attain this object, a method of cutting a workpiece with the aid of a cutting apparatus comprising: at least a first cutting means whose first rotary shaft has a first cutting blade fixed to its end; a second cutting means whose second rotary shaft has a second cutting blade fixed to its end; each first and second cutting blades has a circular cutting edge on its periphery; guide means for holding the first and second cutting means with their center axes aligned in line, and for supporting movably the first and second cutting blades in the confronting relation, thereby permitting them to be fed for indexing; and a chuck table adapted to be moved in the cutting direction perpendicular to the indexing direction, thereby making the first and second cutting edges cut a plurality of parallel lines separated at a predetermined interval in the workpiece while the chuck table is being fed in the cutting direction, is improved in that the method comprises:
the first step of: separating one of the first and second cutting means from the other at such an edge-to-edge distance that the first and second cutting edges may be separated two or more integer xe2x80x9cnxe2x80x9d times the line-to-line distance; putting one of the first and second cutting means in alignment with the particular center line at the center of the intermediate zone of the workpiece, allowing the other cutting means to remain the edge-to-edge distance apart; and cutting the workpiece with the first and second cutting blades simultaneously; and cutting 2n lines every two lines longitudinally every time the first and second cutting means have been fed the line-to-line distance laterally; and
the second step, which is subsequent or antecedent to the first step, of: allotting one of the first and second cutting edge to one of the opposite sides of the intermediate zone and the other cutting edge to the other side to cut two lines longitudinally in the opposite side zones every time the first and second cutting means have been fed the line-to-line distance laterally so that the first and second cutting edges may be brought close to each other or apart from each other.
The workpiece may be a semiconductor wafer having cross streets drawn to draw a lattice pattern on its surface, the workpiece being diced into square chips by cutting crosswise.
Other objects and advantages of the present invention will be understood from the following description of a preferred embodiment, which is illustrated in accompanying drawings.